This invention relates generally to dental syringes, and more particularly to a fitting for releasably connecting a syringe tip to a hand piece for delivering a fluid to a mouth of a patient.
Dental syringes are hand-held devices for discharging fluids, such as pressurized air and water, into a patient's mouth. Syringes typically have a hand piece for gripping by a hand of a dentist or dental assistant and a fitting adapted for receiving a detachable tube or tip. Such syringes are described in U.S. Pat. No. 5,927,975 and U.S. application Ser. No. 09/400,217, filed Sep. 21, 1999, which are hereby incorporated by reference. Fluids are conveyed through the hand piece and the fitting to the tip which delivers the fluids to the patient's mouth. The tip must be securely held by the fitting to prevent it from being ejected into the patient's mouth, and it must be clean to avoid spreading disease. To ensure the tips are clean, dentists typically change tips after each patient.
Ideally, a dentist should be able to quickly and securely lock a new tip in place. Unfortunately, many conventional syringes do not provide this ability. For instance, some fittings require that the tip have a circumferential groove extending around the exterior surface of the tip. These fittings hold the tip in place with ball bearings which engage the circumferential groove. To use these fittings, the dentist must first depress a collar to permit the ball bearings to move radially outwardly so the tip can be inserted, and thereafter allow the collar to return to a locking position wherein the ball bearings are moved inwardly to engage the groove and lock the tip in position. These steps require the dentist to use both hands and can be awkward. Further, if the collar has not properly returned to its locking position, the tip remains loose and may be ejected from the syringe, posing a potential safety hazard. Other fittings hold a tip in place with elastomeric O-rings which engage the circumferential groove. Although these fittings grip the groove automatically when a tip is inserted, they rely on elasticity of the O-rings and friction between the O-rings and the tip to oppose removal of the tip. Because the magnitude of the frictional force is relatively limited, the tip is subject to ejection from the fitting when exposed to a strong force. Further, O-rings degrade over time which can diminish their elasticity and ability to generate frictional force, making the fitting unreliable.
Another type of fitting is adapted for holding a tip which does not have a circumferential groove but rather has an exterior surface that is generally uniform in size and shape along the tip. These fittings frequently include a threaded retainer nut or locking cap which must be screwed on to lock the tip in place. The dentist must unscrew the retainer nut, hold the nut or set it aside while removing a used tip and inserting a clean tip, and then re-attach the retainer nut. These steps are awkward and time-consuming. Other fittings of this type have a collet or the like for gripping the exterior surface of the tip. These fittings can be adequate for some applications. However, when exposed to large forces, such as forces generated when large quantities of high pressure fluid pass through the tip, the grip of the collet may be overpowered and the tip ejected.